面向空间特征的虚拟树木建模方法与应用

树木的三维建模是建立虚拟森林环境的关键问题之一。基于树木形态结构特征分析,提出了面向对象的矢栅混合模型,并详细描述了主干、枝段、枝条和树叶之间的五组拓扑关系。结合L-system s和三维几何结构方法的优势,提出规则和约束的三维树木建模方法,该方法将分枝策略和叶片空间分布特征转化为规则,利用参数化L-system s实现,建模时将树木的空间几何特征和拓扑关系赋予树木模型,所建模型符合树木的生物物理特征。建模过程中通过阈值、模型调整和随机值约束,对模型参数进行控制,约束的内容包括树木结构、单叶尺寸、叶面积指数、随机性四个方面。最后,利用VC++与OpenGL实现了数据模型与建模算法,并利用实测数据进行了验证,所得模型比其他模型更符合于树木实际的形态结构参数和生物物理指标,有利于实现与树木空间结构相关的定性和定量分析。

Modeling Method and Its Application of Virtual Trees in Consideration of the Spatial Features

Three-dimensional modeling of trees is one of the key issues of building virtual forest environment.On the basis of analyses the morphology of trees,an object-oriented vector-raster mixed tree model is proposed.The main components of the trees were seen as vector model and the leaves as raster model in the tree model.The main components of the trees have been abstracted into several classes based on object-oriented thinking.Each vector class is composed of basic vector point,arc,face and body.The model has the obvious level feature.Five topological relations are introduced in detail among trunk,segment,branch and leaf.The three-dimensional modeling method of trees which combines the advantages of both L-systems and three-dimensional geometry framework is proposed base on rules and restriction.In the modeling method branching laws and spatial distribution characteristics of leaves are changed into rules.The tree model is consistent with the biophysical characteristics of trees.And it is provided with space geometrical features and topological relations.Model parameters are controlled by threshold,model adjusting and random restriction.The model achieved a higher precision.Tree restriction involves tree configuration,leaf size,leaf area index and random.Finally the tree model and modeling method are realized by Visual C＋＋and OpenGL.The modeling method is tested by measurement data.The obtained tree model is more in line with the actual morphological structure parameters and bio-physical indicators than any other model.The obtained tree model supports physiological and ecological process simulation,rule discovering,and parameter calculation.